368 
— Floating plants, with very cellular, lenticular, or lobed stems and leaves confounded. 
Flowers appearing from the margin of the stems. 
Affinities. These are plants of a still simpler organisation than Flu- 
viales, like them apparently destitute of spiral vessels, and not producing any 
separate stem or leaves, but a body formed out of both, from within the sub- 
stance of which proceeds a membranous spathe containing one naked male 
and one naked female flower ; a stem and two flowers thus constituting the 
whole of the plant. But if an abstraction be made of the simplicity of this 
structure, and the organisation be considered as if it belonged to plants of a 
more highly developed character, it will be found that these are really nothing 
but Aracese, the spadix of which is reduced to two flowers of different sexes. 
But while the accuracy of this view of the nature of Pistiacese is not likely to 
be questioned, it must be borne in mind that this very reduction of parts is 
inconsistent with the notion of Aracese, properly so called ; and hence the 
necessity of constituting a particular order. I find from an examination of 
seeds of Pistia, most kindly procured from India for me by Dr. Wallich, that the 
embryo is a minute body lying at the apex of the albumen ; in Lemna it 
occupies the axis ; in both there is a fungous testa, with a remarkable indura- 
tion of the foramen of the secundine. The embryo of Pistia is very minute, 
and perhaps solid ; but in Lemna there is the slit on one side for the emission 
of the plumule, just as in Aracese. In Hooker’s Botanical Miscellany, part 2, 
is an account of the germination of Lemna, by Wilson of Warrington, which 
is worth consulting. See for an elaborate account of the seed, &c. of Lemna, 
the Arch, de Botanique, vol. 1. p. 200, by Richard, and the same work vol. 2. 
p. 97, by Adolphe Brongniart. Both should be examined as these two learned 
Botanists are not agreed as to what the structure really is. 
Geography. Lemna inhabits the ditches of the cooler parts of the world ; 
Pistia the tropics. 
Properties. Pistia Stratiotes grows in water-tanks in Jamaica, where, 
according to Browne, it is acrid, and in hot dry weather impregnates the 
water with its particles to such a degree as to give rise to the bloody 
flux. Hist, of Jam. 330. A decoction of the same planFis considered by 
the Hindoostanees as cooling and demulcent, and they prescribe it in cases of 
dysuria. The leaves are also made into a poultice for the piles. Ainslie. 
GENERA. 
Pistia, L. Lemna, L. 
Group VI. 
Essential Character. — Perianth usually 0, in its room herbaceous or scarious bracts, 
imbricated over each other ; if present surrounded by such bracts. 
These are distinctly characterised by the want of a true perianth, in the 
room of which the floral envelopes are formed by imbricated bracts. The 
palese of Grasses approach the nature of a calyx ; but as they do not originate 
from the same plane, they cannot, practically, be confounded with a calyx, 
however near such an organ they may, upon theoretical principles, be consi- 
dered to approach. The same may be said of the hypogynous setae of Cype- 
raceae, which, although probably of the nature of a perianth, exist in so 
rudimentary a state as not to form a real exception to the character of Gluma- 
ceae. Restiaceae and Palms connect petaloideous Monocotyledons with Glumar 
